AN ECLIPSE EXPEDITION TO SPAIN 



559 



More than Two Thousand Years Old. 



of a triangular prism of glass which breaks up the white light of the sun 

 into its component colors of red, orange, yellow, green, blue, indigo 

 and violet. The other and better way is by the use of a grating. Such 

 at. instrument is made by ruling on the surface of a plane or concave 

 mirror many thousand tine lines separated by equidistant intervals. 

 The writer had mounted for his use at the eclipse five spectroscopes, two 

 being prisms, the others gratings. By means of these a great variet}* - 

 of problems were attacked, such as the constitution of the atmosphere 

 immediately surrounding the sun and the heights in miles to which the 

 different gases extend above the sun's surface, the nature of the gases 

 that go to make up the beautiful corona, the amount of heat and 

 energy of the corona, etc. 



